1. Field of the Invention
The present invention relates to a hall effect-sensing apparatus for moving object enabling to detect moving status of a moving object such as a rack in a rack and pinion mechanism, a gear, or a multipolar magnet which moves straightforwardly or rotationally.
2. Description of the Prior Art
It has been conventionally known of a moving object detecting apparatus which has a structure as in FIG. 18. This apparatus can detect a moving status such as a moving distance or moving speed of a moving object which moves straightforwardly or rotationally. (Japanese Patent Laying-Open No. 2-264817)
The moving object detecting apparatus shown in FIG. 18 is comprised of: a cylindrical case 31, a lid 32 having a flat top surface 32a which is positioned on the top of the case 31, a detecting means 40 employing a detecting element 33 which is fixed inside the top surface 32a, and a filler 39 supporting the detecting means 40 in the case 31.
The detecting element 33 includes a pair of magnetic/electric conversion elements such as Hall elements 33a and 33b in keeping a distance L. In the detecting means 40, the detecting element 33, a magnet 35 providing a magnetic field to the Hall elements 33a and 33b, and a yoke 36 making a magnetic circuit which is positioned beneath the magnet 35 are assembled such as forming a layer.
This yoke 36 is used in order to increase magnetic coupling between the Hall elements 33a and 33b and the magnet 35 and, as a result, to heighten the detecting sensitivity of the detecting element 33.
There are three leads 33A, 33B, and 33C which are connected to the detecting means 40. Each of the leads 33A, 33B, and 33C is connected to an outside test device 41 through a cable 37.
An operation of the detecting means 40 is described in the following. Flux densities B.sub.a and B.sub.b are applied to the pair of the Hall elements 33a and 33b which are mounted on the detecting element 33 by the magnetic field of the magnet 35. Each Hall element 33a and 33b outputs voltage depending on the flux densities B.sub.a and B.sub.b. The voltage outputted from the Hall elements 33a and 33b is processed in a processing circuit 33c which is assembled in the detecting element 33 and outputted as a detecting signal. Namely, by means of the processing circuit 33c assembled in the detecting element 33, when a difference of the flux density .DELTA.B (=.DELTA.B.sub.a -.DELTA.B.sub.b) between the pair of the Hall elements 33a and 33b becomes larger than a certain upper threshold (.DELTA.B.sub.1), the output level of the detecting signal goes down to L-level as shown in FIG. 19. Further, when a difference of the flux density .DELTA.B becomes smaller than a certain lower threshold (.DELTA.B.sub.2), the output level of the detecting signal goes up to H-level. Thus, the magnetic characteristic of the detecting element 33 is determined by these threshold values in the upper threshold (.DELTA.B.sub.1) and the lower threshold (.DELTA.B.sub.2). The difference of the flux density .DELTA.B is caused by a variation of the flux densities B.sub.a and B.sub.b which are applied to the Hall elements 33a and 33b by irregularity of teeth 38a of a magnetic moving object 38 which is positioned near the detecting means 40.
The above moving object detecting apparatus can detect a moving distance and speed of the moving object 38 by the test device 41 by positioning the teeth 38a of the moving object 38 near the top surface 32a, and by moving the moving object 38 in a X-direction so that the detecting means 40 generates the signal depending on the irregularity of the teeth 38a. Namely, when the moving object 38 moves to the X-direction, the output power from the Hall element 33a and 33b is processed by the detecting means 40, and a pulse signal as in FIG. 19 is generated from the detecting means 40 as the detecting signal. Thus, the moving distance and the speed of the moving object 38 can be obtained by counting a number of pulse per unit time of the detecting signal which can be obtained from the detecting means 40.
In the conventional moving object detecting apparatus; however, the detecting sensitivity is lowered due to variance in the magnetic characteristic of the detecting element 33 and the magnet 35 composing the detecting means 40.
Namely, the Hall elements 33a and 33b, which are positioned inside the detecting element 33 as the pair of magnetic/electric conversion elements, are formed on a substrate by a film of various semiconductor materials. However, the Hall elements 33a and 33b sometimes are not formed on the substrate to match their magnetic characteristics. In addition, the processing circuit 33c which processes the output power from the Hall elements 33a and 33b is also subjected to a dispersion to the magnetic characteristics due to the dispersion of values in circuit components. As a result, when the magnetic characteristic of the detecting element 33 fluctuates, that is, when the upper threshold .DELTA.B.sub.1 ' and the lower threshold .DELTA.B.sub.2 ' are shifted to the upper direction as shown in FIG. 20, the pulse as shown in FIG. 19 is no longer generated from the detecting means 40, and thus the detecting sensitivity is lowered.
Even if the upper threshold .DELTA.B.sub.1 and the lower threshold .DELTA.B.sub.2 do not fluctuate, the magnetic field of the magnet 35 is sometimes unstable. This causes an unbalance in the flux densities B.sub.a and B.sub.b which are applied to the pair of the Hall elements 33a and 33b. When, for example, the difference of the flux density .DELTA.B' is fluctuated to the lower direction as shown in FIG. 21, the pulse shown in FIG. 19 cannot be outputted and the detecting sensitivity is accordingly lowered.
This unbalanced flux densities B.sub.a and B.sub.b are equally caused by an irregular position of the Hall elements 33a and 33b inside the detecting element 33 or an irregular mounting position of the detecting element 33 against the magnet 35.
In addition, in the conventional moving object detecting apparatus, since there is a problem that components such as detecting element 33, the magnet 35, and the yoke 36 tend to fall from the apparatus in an assembling process, the assembling efficiency as well as the detecting sensitivity will decrease.